function check() {
    var sec=$('#secend').val(); //获取箱子布局
    var fir=$('#first').val();
    if (fir==!0||sec==0) {
        $('#lert').html("<div class='alert alert-error'><h4>请选择箱子布局.</h4></div>");
        return false;
    } else {
        return true
    }
}
var doorLayout = [
    ["一行两列", "两行一列"],
    ["两行两列", "一行四列", "四行一列"],
    ["三行两列", "两行三列"],
    ["四行两列", "两行四列"],
    ["两行五列","五行两列"],
    ["三行四列","四行三列"]
];

function getNum() {
    var doorsnum = $('#first').val();
    var doorslayout = $('#secend').val();

    var layout=doorsnum/2-1;
    var shu=doorLayout[layout];
    var html="<option value='0'>请选择箱子布局</option>";
    $.each(shu,function(key,val){
        html+="<option value='"+val+"'>"+val+"</option>";
    });
    $("#secend").html(html);
}